Support loading a different pryrc from ENV
Support loading a different pryrc from ENV

If the user exports $PRYRC, assume that's the end-user configuration file, and
load that instead of `~/.pryrc`. Closes #893.

raeno/pry,raeno/pry,jasonm23/pry,ngpestelos/pry,nju520/pry,shockone/pry,geoffreylitt/pry,richo/pry,icebreaker/pry,sferik/pry,bronzdoc/pry,pvdb/pry,gfvcastro/pry,jasonm23/pry,nju520/pry,ooohiroyukiooo/pry,gfvcastro/pry,raeno/pry,shockone/pry,scalixte-mdsol/pry,printercu/pry,85x14/pry,tdg5/pry,caporta/pry,ooohiroyukiooo/pry,85x14/pry,sideci-sample/sideci-sample-pry,jasonm23/pry,85x14/pry,sferik/pry,geoffreylitt/pry,shockone/pry,jasnow/pry,printercu/pry,tdg5/pry,deivid-rodriguez/pry,ooohiroyukiooo/pry,nju520/pry,bronzdoc/pry,jasnow/pry,ngpestelos/pry,scalixte-mdsol/pry,josue804/debunker,pvdb/pry,scalixte-mdsol/pry,josue804/debunker,jasnow/pry,caporta/pry,caporta/pry,icebreaker/pry,tdg5/pry